“…Many published algorithms for optic disc detection [12,19,65], image registration [5,41,45,52,59,69,71], change detection [16,18,21,22,50,58,70], pathology detection and quantification [25], tracking in video sequences [33,43,55], and computer-aided screening systems [29,46,60,68] depend on vessel extraction. The techniques published in the research literature in response to the importance of retinal vessel extraction may be roughly categorized into methods based on matched filters [8,20,43], adaptive thresholds [20,24], intensity edges [4,32], region growing [40], statistical inferencing [38], mathematical morphology [18,40,72], and Hessian measures [3,25,56,57]. This wide range of techniques closely corresponds to the suite of methods that have been applied throughout the medical image analysis literature [28].…”